Strain-rate effect of polymers and correction methodology in a SHPB test

Split Hopkinson pressure bar (SHPB) has been commonly used to characterize the dynamic behavior of polymer at high strain-rates from 10² to 10⁴ s⁻¹. Based on numerical SHPB tests and Drucker-Prager model, this study examines the SHPB technique for the measurement of the dynamic strength of polymers, which is hydrostatic pressure sensitive. It is shown that the enhancement of the apparent dynamic strength above 10² s⁻¹ strain-rate is influenced considerably by the lateral inertia confinement in the SHPB specimen. This phenomenon is accompanied by the change of the stress state (i.e., from a uniaxial stress state to a multi-axial stress state) in the SHPB specimen when the strain-rate is larger than the transition strain-rate. An iterative correction methodology is employed to identify the actual strain-rate effect. The proposed method is verified using a typical polymer of polycarbonate and can be applied to other polymers.